1. Field of the Invention
The present invention relates generally to methods of manufacturing heat exchanger tubes and, more particularly, to a method of cutting flat tubes into unit pieces for heat exchanger.
2. Description of the Prior Art
Flat tubes of a heat exchanger of the parallel flow type, for example, have one or more refrigerant passages therein. Such flat tubes are made by forming by extrusion a continuous tube and then cutting it into unit pieces with a tube cutter which is provided on a conveyor line. The height and the width of the continuous tube are adjusted either before or after the cutting step.
The conventional cutting techniques include (1) a metal cutting process; (2) a press cutting process; (3) a laser cutting process; and (4) a process which includes forming circumferential grooves on the continuous tube with a rotary cutter and applying a tension to the continuous tube to break it into unit pieces at the circumferential grooves. See Japanese Patent Application Kokai No. 63-264218.
In the metal cutting process, not only chips or sawdust is produced but also undesirable burrs are formed on the cut surface. As a result, a considerable number of refrigerant passages in the unit pieces are choked with the sawdust and/or closed by the burrs. For this reason, the metal cutting process requires an additional burring step, resulting in the increased unit manufacturing cost.
In the press cutting process, the cut plane of a unit piece is susceptible to deformation due to collapse of the refrigerant passage under the press action. Also, it is often that burrs are formed on the cut plane. For these reasons, this process requires not only a burring step but also a passage expansion step, resulting in the increased unit manufacturing cost.
The laser cutting process relies on the thermally fusing action of laser for cutting a continuous tube so that part of the fused material deposits on the cut surface of a unit piece. For this reason, a step of removing such deposits is required, increasing the unit manufacturing cost.
The last process mentioned above which includes forming cutting grooves on the continuous tube with a rotary cutter and applying a tension to the continuous tube pull it into unit pieces at the cutting grooves, has a disadvantage particularly for flat tubes into which the cutter blade tends to cut through, forming burrs and choking some of the refrigerant passages as in the press cutting process. In addition, the continuous tube is pulled into unit pieces by the rollers in the direction of travel of the tube so that the cut planes have rough surfaces, requiring an additional finishing step, resulting in the increased unit manufacturing cost.